Milo g



(No Model.)

M. G. KELLOGG. MULTIPLE SWITGHBOARD.

No. 592,388. Patented Oct. 26,1897.

llnrrnn STATES PATENT FFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGGSVVITGIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

, MULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,388, dated October26, 1897. Application filed August 5, 1890. Serial No. 361,115. (Nomodel.

To (LZZ whom it may concern:

Be it known that I, MILO G. KELLOGG, of Chicago, in the county of Cookand State of Illinois, temporarily residing at Stuttgart, in the Empireof Germany, have invented certain new and useful Improvements inMultiple Switchboards for Telephone-Exchanges, of which the following isa full, clear, concise, and exact description, reference beinghad to theaccompanying drawings, forming a part of this specification.

My invention relates to a metallic-circuit telephone-exchange system inwhich there is a plug and a cord attached for each line of the exchange.Such asystein is called a single-core system. Said plug normally restsin a switching device, and when it is desired to connect the line withanother line the plug is taken from its normalposition and is placed inthe switch of the other line.

My invention consists in an organization of apparatus, circuits, andconnections for each line whereby the operator may expeditiously andwith few motions connect her telephone to a line when its call isindicated, may test the line wanted, may connect the two lines togetherand send a calling-current to the line wanted, may leave the linesconnected together for conversation and connect her telephone into theircircuit to determine whether they are through conversation, and mayreceive and attend to any clearing-out signal. Said organization is moresimple and the operations required are less than in other sys temsdevised to accomplish similar purposes.

In the accompanying drawings, illustrating my invention, Figure 1represents the centraloffice apparatus and connections, and Fig. 2 thesubscrihefis-station apparatus necessary to illustrate my invention.

In the central office are as many switchboards as are found necessary ordesirable in order to properly operate the exchange.

In Fig. 1, AA represent sectional views of sections of two switchboardsto which the same lines connect. On each board of the exchange is aspring-jack or similar switch for each line. Each switch has acontactspring which is normally in contact with a contact-point and isseparated and insulated from the point when a switch-plug is insertedinto the switch, and has a third contactpiece which is normallyinsulated from the otherparts, except by the circuit connections. Thiscontact-piece is adapted to have a testplug applied to it for testing.The switches shown in the figure are of well-known construction. Foreach line there is also a compound answering switch or device located atthe board where the cord and plug of the line are located and where itscalls are to be answered. This answering switch or device is operated onin part by the switch-plug when placed in its normal position and inpart by the operator who answers the calls of the line. Theconstruction, operation, and manipulation of these answering switches ordevices will hereinafter be explained in detail.

Two lines and their switches on the boards, their plugs and cords, theircompound answering-switches, and their annunciators are shown in Fig. 1.The answering apparatus of one line is shown as located at one board andthat of the other line at the other board.

B B represent the two compound answeringswitches of the lines, and D Dtheir switchplugs, to which the double insulated flexible conductors areattached. These plugs are adapted to be placed in any switch at theirboards and are each adapted to he placed normally,or when not in use, inthe answering switch of its line and to operate the switch, as will bedescribed. One plug is shown in its answering-switch and the other isshown out of its switch. In the said switches, BB do are cylinders,preferably of metal, adapted to receive and guide the commutator andplugsupporting pieces I) I). These pieces I) b (one for each switch) maybe of rubber and of the shape substantially as shown or of other shapesto correspond with variations in the shape and arrangement of the otherparts of the switches. 1, 2, 3, 4, 5, 6, and 7 are contactpiecesinsulated from each other. 2, 4, and 5 are spring contactpieces. Theother pieces may be rigid. Pieces 1 and 2 are mounted parallel to eachother and in close juxtaposi tion,so that contact between them will bemade and broken by the operation of the switchplug, as hereinafterindicated The pairs of contacts 3 4 and 5 6 are mounted parallel to eachother and in close juxtaposition, so that the plug.

the contact of each pair is made and broken, as hereinafter described,by the operation of Spring 4 is connected near its upper end to spring 5by means of an insulationpiece fastened to both. It therefore moves backand forth as spring 5 moves.

toward the center of piece I) and will press against and be acted uponby the plug, as will be described.

The piece 1) has a hole or socket in its top adapted to receive theplug-handle. It has also two chambers at its sides adapted to receivethe bent portions of springs 2 and 5, as shown, and has also a shoulderadapted to rest on the piece a when the piece I) is moved to itslower'position. In the chamber adapted to receive the bent part ofspring 5 is a shoulder or projection c, on which the spring 5 bears whenpiece b is moved to its upper position, and which then causes contactsto change, as will hereinafter be indicated. These pieces I) b areadapted and intended to occupy two positions in the operation of thesystemthe upper or outer position, as shown in B, and the lower or innerposition shown in 'B.

' When the switch-plu g is in its socket in the movable piece I), thispiece should-occupy its lower position and the handle of the plugpresses on the springs 2 and 5, so that spring 2 is brought into contactwith piece 1 and is not in contact with piece '7, and spring 5 ispressed'out of contact with piece 6, while spring 4, which is attachedto but insulated from 5, is pressed out of contact with piece 3. Whenthe plug is withdrawn from the socket f by the operator, the springs 2and 5 are released from the pressure of the plug-handle and (the movablepiece 19 being still in its 1 lower position) the contact between 2 and1 is broken'and contacts between 2 and 7, be-

tween 3 and 4, and between 5 and 6, respectively, are established.

WVhen the plug is removed from the socket and the operator manipulatespieceb and places it in its upper position, the contact between 2 and 7still re mains and the shoulder c in the chamber of the piece I) pressesspring 5 out of contact with piece 6, and at the same time spring 5carries spring 4 out of contact with piece 3.

When, therefore, the plug is in its socket and piece I) is raised to itsouter position 7 and 2 are in contact and all of the other pairs ofcontacts are out of contact.

The switch-plugs D D are of a usual construction of loop-switch plugsadapted to be used with the spring-jack switches. The outsides of thehandles have a rubber insulation.

Springs 2 and 5 are constructed and adjusted to press Each plug has twoswitch contact-pieces insulated from each other, one of them, 3, beingat the end of the plug-tip and the other, 3, being an insulated cylinderplaced along the surface of the tip. WVhen a plug is inserted into aswitch, the piece .9 presses against the spring of the switch and forcesit away from the contact-point and makes a connection with it, and theother piece of the plug (8) forms connection with the third or insulatedcontact-piece of the switch.

25 t are operators telephones; R R, operators calling-batteries; r r,resistance-coils, and K K calling-keys. Each operator has one of each ofsaid parts, and they are connected to each other and to heransweringswitches substantially as shown and as will be described.

w and 5c are calling-annunciators, one for each line shown. Theannunciators are preferably polarized annunciators.

G G are ground connections.

y y are retardation-coils, one for each line of the exchange.

R is a test-battery.

The calling-keys K K are three-point keys having each a lever and twopoints, on one of which the lever normally bears and on the other ofwhich it is in contact when it is pressed down by the operator away fromthe first-mentioned poin-t'.

.Each of the retardation-coils contains two spools or helices ofinsulated wire, each helix surrounding an iron core. The two cores areconnected at their two ends by cross-bars of iron. The coils of aretardation-coil are connected together in such a direction as tomagnetizein the same directionthe closed magnetic circuit made by theiron pieces of the coil.

The connections are'substantially as follows: One side or branch of eachline passes normally successively through thepairs of contact-points ofthe line-switches, passing in each case to the spring first. It thenpasses through the line-annunciator and is then connected through one ofthe insulated conductors of the switch-cord to the contact-piece s ofthe switch-plug. The other side or branch of the line is connected toall of said third insulated contact-pieces of the switches of the lineand is connected through the other conductor of the switch-cord to theother contactpiece 8 of the switch-plug of the line. The first-mentionedside or branch of the line is also connected, after it passes throughthe line-annunciator, to contact-pieces 2 and 5 of the compoundanswering-switch of the line, and the other side or branch of the lineis connected to piece 3. One side of the operators telephone isconnected to the contact-piece 4 of the answering-switch, and the otherside of the telephone is connected, through the resistance-coil, tocontactpiece 6.

The circuit-wire connecting the telephone and contact-piece 4 isconnected to the upper contact-point of the calling-key. The lower IICnected, through the retardation-coil of its line and thence through thecommon test-battery to the ground. Piece 1 is grounded.

Each compound answering-switch is connected to its line and to theoperators special apparatus substantially as described. It is alsoconnected to its retardation-coil and to the test-battery, as described.One testbattery will answer for all of the lines of the exchange.

In the subscribersstation apparatus shown in Fig. 2, 1 is thetelephone-switch. 2 is the calling-generator. 3 is the signal-receivingbell. l is the operators telephone, and 5 is a resistance-coil.

coil are placed in a ground-Wire which is connected to a contact-pointof the switch. This contact-point is in contact with the switchleverwhen the telephoneis on the switch, and the line-circuit is groundedthrough the bell and resistance-coil when the telephone is on theswitch, and said ground connection is open when the telephone is off theswitch. Other arrangements of contacts and points may be used which willproduce the same result. The bell could, if'desired, be removed fromsaid ground-wire and be placed in the line-circuit.

The calling-generator is connected into the line-circuit so that it isbetween the normal ground connection at the subscribers station and thenormal ground connection of the line at the central office.

The operation of the system is as follows: \Vhen the plug of a line isin its normal position in the socket of its compound answeringswitch andthe line is not switched at any board of the exchange, the line isgrounded at the central office. \Vhen the line is switched at any boardby the insertion of a switch-plug into its switch or its plug iswithdrawn from its normal position in the socket, the said groundconnection is broken. In the latter case the interruption is at the pairof contacts 1 2 and in the former case in the pair of contact-points ofthe switch. 'When the plug is withdrawn from its normal position in theanswering-switch, the line is grounded through its retardation-coil andthe testbattery by the closing of contacts 2 and 7 and the two sides ofthe line are automatically brought into a closed circuit, with theoperators telephone in the circuit. This connection is made by theclosing of the two pairs of contacts 3 at and 5 6, respectively. Suchcircuit is from contact-spring 5 (which is connected to one side of theline) to contact piece Z), and thence through the resistancecoil 4' andoperators telephone t to the contact-piece 4:, and thence tocontact-piece 3, which is connected to the other side or branch G is aground connection. The signal-receiving bell and the resistanceof theline. The operator then by conversation finds out what line is wanted bythe subscriber. She then tests the line wanted, as will hereinafter bedescribed, and if she finds it to be free she places the switch-plug inits switch. The two lines are then connected together into a metalliccircuit, and the circuit is cross-connected or bridged by a circuitwhich contains the resistance-coil and telephone. The operator thereuponpresses down on the lever of her calling-key and thereby connects hercalling-generator in a circuit from the ground to the line-circuit andto ground at the station of the subscriber wanted, and his signal-bellwill be rung. The telephone of the calling subscriber will generally beswitched for use during this operation, and his bell will not ring. Theoperator then moves the piece 1) of the answeringswitch to its upper orouter position, and the bridge circuit or connection of the circuit isopened by the opening of the pairs of contactpoints 3 4; and 5 6.

When the operator desires to listen into the circuit to determinewhether the subscribers are through conversation, she presses themovable piece I) in and thereby establishes again the bridge to thecircuit which contains her telephone and resistance-coil. Theresistance-coil prevents an undue amount of the telephone-current fromgoing through her telephone.

The test system is as follows: When any line is unswitched at any board,it is disconnected from the ground connection through the test-battery.WVhen it is switched at any board,either by its own switch-plug beingused for switching or the switch-plug of another line being insertedinto one of its lineswitches,its circuit is connected to the groundthrough the test-battery. The connection is made by the closing of thepair of contactpoints 7 2 of the answering-switch used in switching.Then the line is not switched, it is not ground ed through a battery.\Vhen the operator desires to test any line to find out whether it isswitched, she places the tip of the switch-plu g of the callin g-line onthe insulated contact-piece of the switch at her board of the line to betested. If the line is switched at anyboard, there is a complete circuitthen established through the test-battery and the operators telephonewill sound or respond. This circuit is from the ground at the centralollice of the line tested through its test-battery and retardation-coiland the pair of 0011- tacts 2 7 of the line Whose plug has been used inswitching the line tested, thence to contact 8 of said plug, thencethrough the circuit of the line by way of the subscribers station to theswitch-contact to which the test is applied, and thence through thecontact-piece s of the plug used in testing and contacts 5 6 of itsswitching device, the resistance-coiloythe operators telephone 6, andthe normally closed contacts of the key K to ground. If the line is notswitched, there is no such circuit estab- .is broken and the line islished and the telephone will not respond. She can therefore tellwhether or not the line is switched 'at'any board.

It will be noticed that when two lines are connected for conversationtheir circuit is grounded at the central office through a retardation-coil and the test-battery. The retardation-coil prevents orminimizes the efiect on the circuit which might arise from othermetallic circuits connected in like manner to the ground.

I use'the terms bridge and cross-connect in connection with a completemetallic I circuit to describe a connection between one side or branchof the circuit and its other side or branch, and an instrument in abridge or cross-connecting circuit to a metallic cirnormally-grounded atthe central office, lIlf combination with a switch-plug with cord for fsaid line, a test-wire grounded on one side, a

test-battery, in said test-wire, a switching d'e- Q vice into which theplug is normally. placed, a pair of contacts in' said switching devicenormally open but closed on the withdrawal of the plug, to one of whichsaid line is connected and to the other of which the other side i ofsaid test-wire is connected anda pair of contacts through which saidlinenormally passes, i

normally closed but open on the withdrawal of the plug, by which whenthe plug is withdrawn fromthe switching'device the said normal groundconnection of the line is broken 7 and the line isgrounded through thetest-bat- 'tery, substantially as set forth.

2. In atelephone-exchange system, a metallic-circuit line one side orbranch of which is normally grounded at the central office, incombinationwith a switch-plug with cord for saidline, a circuit-wiregrounded at one end,

'a retardation-coil in said circuit-wire, and a 3 switching device intowhich the plug is normally placed,a pair of contacts in said switchingdevice normally open but closed on the vwithdrawal of the plug, to oneof which said line is connected and to the other of which the other endof said circuit-wire is connected and a pairof contacts through whichsaid line normally passes, normally closed but open on the withdrawal ofthe plug, by which when the plug is withdrawn from the switching devicethe said normal connection of the line grounded through theretardation-coil,substantially as set forth.

3'. Ina telephone-exchange system, ametalli'ccircuit line one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wiregrounded at one end, a test-battery and retardation-coil in saidcircuit-wire and a switching device into which the plug is normallyplaced, a pair of contacts in said switching device normally open butclosed on the withdrawal of the plug to one of which said line isconnected and to the other of which the other end of saidcircuitwire isconnected and a pair of contacts through which said line normallypasses, normally closed but open on the withdrawal of the plug, by whichwhen the plug is withdrawn from the switching device the line isgrounded through the test-battery and retardation-coil, substantially asset forth.

4. In a telephone-exchange system, a metallic-circ uit line one side orbranch of which is norm ally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wiregrounded at one end, a test-battery in said circuit-wire, a switchingdevice into which the plug is normally placed,

a pair of contacts in said switching device normally open but closed onthe withdrawal of the plug, to one of which said line is connected andto the other of which the other end of said circuit-wire is connectedand a pair of contacts through which said line normally passes, normallyclosed but open on the withdrawal of the plug, by which when the plug iswithdrawn from the switching device such normal connection of the lineis broken and the line is grounded through a test-battery, and a testreceiving instrument grounded on one side and connected on its otherside to a plug or device adapted at the will of the operator to bebrought into connection with the line, substantially as set forth.

5. In a telephone-exchange system, a metallic-circuit line one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wiregrounded at one end, a test-battery and retardation-coil in saidcircuit-wire, a switching device into which the plug is normally placed,a pair of contacts in said switching device normally open but closed onthe withdrawal of the plug, to one of which said line is connected andtothe other of which the other end of said circuit- Wire is connected, anda pair of contacts through which said line normally passes, normallyclosed but open on the withdrawal of the plug by which when the plug iswithdrawn from the switching device such normal connection of the lineis broken and the line is grounded through a test-battery, and a testreceiving instrument grounded on one side and connected on its otherside to a plug or device adapted at the will of the operator to bebrought into connection with the line, substantially as set forth.

6. In a telephone-exchange system, a metallic-circuit line one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wireconnected at one end to one side of a test receiving instrument, atest-battery in said circuit-wire and a switching device, a pair ofcontacts in said switching device normally open but closed'on thewithdrawal of the plug, to one of which said line is connected and tothe other of which the other end of said circuit-wire is connected and apair of contacts through which said line normally passes, normallyclosed but open on the withdrawal of the plug by which when the plug iswithdrawn from its normal position in the switching device the normalground connection of the line is broken and the line is connected to oneside of said testbattery, substantially as set forth.

7. In a telephoneexchange system, a metallic-circuit line one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wireconnected at one end to one side of a test receiving instrument, aretardation-coil in said circuit-wire, and a switching device, a pair ofcontacts in said switching device normally open but closed on thewithdrawal of the plug, to one of which said line is connected and tothe other of which the other end of saideircuit-wire is connected and apair of contacts through which said line normally passes normally closedbut open on the withdrawal of the plug by which when the plug iswithdrawn from its normalposition in the switching de-' vice the normalground connection of the line is broken and the line is connected to oneside of said test-battery, substantially as set forth.

8. In a telephone-exchange system, a metallic-circuit line one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wireconnected at one end to one side of a test receiving instrument, atest-battery and retardation-coil in said circuit-wire, and a switchingdevice, a pair of contacts in said switching device normally open butclosed on the withdrawal of the plug, to one of which said line isconnected and to the other of which the other end of said circuit-wireis connected and a pair of contacts through which said line normallypasses normally closed but open on the withdrawal of the plug by whichwhen the plugis withdrawn from its normal position in the switchingdevice the normal ground connection of the line is broken and the lineis connected to one side of said test-battery, and retardation-coil,substantially as set forth.

9. In a telephone-exchange system, a me tallic-circuit line one side orbranch of which is normally grounded at the central ofice, incombination with a switch-plug with cord for said line, a circuit-wire,a test-battery in said circuit-wire, a switching device into which theplug is normally placed, apair of contacts in said switching devicenormally open but closed on the withdrawal of the plug, to one of whichsaid line is connected and to one of which the other end of saidcircuit-wire is connected and a pair of contacts through which said linenormally passes normally closed but open on the withdrawal of the plug,by which when the plug is withdrawn from the device the normal groundconnection of the line is broken and the line is connected to one end ofsaid circuit-wire, and a test receiving instrument connected on one tothe other end of said circuit-wire and on its other side to plug ordevice adapted to be brought into connection with the line,substantially as set forth.

10. In a telephone-exchange system, a metallic-circuit line one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a test-batteryand retardation-coil, a switching device into which the plug is normallyplaced, with contacts and connections by which when the plug iswithdrawn from the device the normal ground connection of the line isbroken and the line is connected to one side of said test-battery andretardation-coil, and a test receiving instrument connected on one sideto the other side of said test-battery and retardation-coil and on itsother side to a plug or device adapted to be brought into connectionwith the line, substantially as set forth.

11. In a telephone-exchange system, a metallic-circuit line, one side orbranch of which is normally grounded at the central office, incombination with a switch-plug with cord for said line, a circuit-wire,a retardation-coil in said circuit wire, a switching device into whichthe plug is normally placed, a pair of contacts in said switching devicenormally open but closed on the withdrawal of the plug, to one of whichsaid line is connected and to one of which the other end of saidcircuit-wire is connected and a pair of contacts through which said linenormally passes normally closed but open on the withdrawal of the plug,by which when the plug is Withdrawn from the device the normal groundconnection of the line is broken and the line is connected to one end ofsaid circuit-wire, and a test receiving instrument connected on one sideto the other end of said circuit-wire, and on its other side to a plugor device adapted to be brought intoconnection with the line,substantially as set forth.

12. In a telephone-exchange system, a metallic-circuit line which isnormally grounded at the subscribers station, one side or branch ofwhich is normally grounded and the other side or branch of which isnormally open at the central office, in combination with a switch-plugwith cord for said line, a test-bat tery, a switching device into whichthe plug is normally placed, with contacts and connections by which whenthe plug is withdrawn from the device the normal ground connection ofthe line at the central ofiice is broken and the line is groundedthrough the test-battery, and a test receiving instrument grounded onone side and connected on its other side to a plug or device adapted tobe brought into connection with said normally as set'forth.

open side or branch of theline, substantially 13. In atelephone-exchange system, a me-i tallic-circuit line which is normallygrounded at the subscribers station through a -resist ance, one side orbranch of the line being nor mally grounded and the other side or branchceiving instrument grounded on one side and connected on its other sideto a plug or dea viceadapted to'be brought into connection withthenormally open side or branch of the line, substantially assetforth.149111 a telephone-exchange system,a me-Q tallic-circuit line which isnormally'grounded at the subscribersstation, one side orbranch; of whichis normally grounded and the other} side or branch normally open at thecentral office, :in combination witha switch with con-i tac-ts andconnections by which such normal ground connectionat the subscribersstation;

is broken while the-.subscribers telephone is switched for conversationa switch-pin g with; cord for the line, a switching device into whichwtheplug isnormally placed,with contacts and -connections by which whenthe plug is with-Q -.drawn.from the switchingdevice the normal;ground-connection of the line at the central;

office vis broken and the" line is grounded -=th:rough.a circuitconnection which containsjl a testabattery and retardation-coil, and atestfl -receiving: instrument grounded on one side: andconnected on itsother side to a plug or'; device adapted to be brought into connection:-1Wl'[ ll the normally openside or branch of the 1ine,.su-bstantially asset forth.

r 15. In.a telephone-exchangesystem,a me-i: tallic-circuit line one sideor branch of which "is .normally grounded at the central office, in

. combination with a switch-p111 g with cord for :theline, atest-battery and retardation-coil, -a.switchin g device into which theplug isnor- :bytwhich when the plug is withdrawn from.

mally placed,v with contacts and connections the-device the normalground connection of.

the line-is .brokenand the line is connected torone side'of a circuitconnection containing 1 test-receiving instrument connected on. one

thetest-battery and retardation-coil, and a side to the other side ofsuch circuit connec-E ,tioneandon .its other side to a plug ordeviceadapted to be brought into connection with the line, substantially asset forth. 16. Ina telephone-exchange system a-mei tallic-circuit linenormally grounded at the subscribers station and one side or branch ofvwhich is normally grounded at the central office, in combination with aswitch at the subscribers station with contacts to open the groundconnection there while thesubscribers telephone is switched for use, aswitchplug with cord for said line, a test-battery, and a switchingdevice into which the plug is normally placed, with contacts andconnections by which when the plug is withdrawn from the switchingdevice the said normal ground connection of the line is broken and theline is grounded through the test-battery,

substantially as set forth.

17. In a telephone-exchange system, a metallic-circuit line normallygrounded at the subscribers station and one side or branch of which isnormally grounded at the central office, in combination with a switch atthe :subscribers station with contacts to open the ground connectionthere while the subscribers telephone is switched for use, aswitchplugwith cord for said 'line, a retardation-coil and'a switching device intowhich the -,plug is normally placed, with-contacts and connections bywhich when the plug is withdrawn from the switching device the saidnormal connection of the line is broken. and the line is groundedthrough the retardation-coil, substantially as set forth.

l8. Ina telephone-exchange system, a metallic-circuit line normallygrounded at the subscribers station and one side or branch of -which isnormally grounded at the central office,in combination .with a switch atthe sub scribers stationwith contacts to open the ground connectionthere while the subscriberstelephone is switched for use, a-switchplugwith cord forsaid line, a test-battery and retardation-coil, and aswitching device intowhich the plug is normally placed, with contactsandconnections by which when the plug is withdrawn from the switchingdevice such normal. ground connection of the line is broken and the'lineis grounded through the test-battery .and retardation-coil,substantially as set forth.

19. In a telephone-exchange system,ame- :tallic-circuit line normallygrounded at the subscribers station and one side or branch of which isnormally grounded at the central ofiice,incombination with a switch atthe subscribers station with contacts to open the ground connectionthere while the subscriberstelephone is switched for use,a switchplugwith cord forsaid line, a test-battery, a

switching device into which the plug is normally placed,'with contactsand connections by which when the plug is withdrawn from the switchingdevice such normal connection .of the lineis broken and the line isgrounded through a, test-battery, and a test receiving instrumentgrounded on one-side and connected on its other side to a plug or deviceadaptedat the will of the operatornto 'be brought intoconnectionwith theline, substantially as set forth.

IOC

20. In a telephone-exchange system, a metallic-circuit line normallygrounded at the subscribers station and one side or branch of which isnormally grounded at the central oftice,in combination witha switch atthe subscribers station with contacts to open the ground connect-ionthere while the subscribers telephone is switched for use, a switchplugwith cord for said line, a test-battery and retardation-coil, aswitching device into which the plug is normally placed, with contactsand connections by which when the plug is withdrawn from the switchingdevice such normal connection of the line is broken and the line isgrounded through said test-battery and retardation-coil, and a testreceiving instrument grounded on one side and connected on its otherside to a test plug or device adapted to be brought into connection withthe line, substantially as set forth.

21. In a telephone-exchange system, a metallic-circuit line, normallygrounded at the subscribers station and one side or branch of which isnormally grounded at the central office, in combination with a switch atthe subscribers station with contacts to open the ground connectionthere while the subscribers telephone is switched for use, a switchplugwith cord for said line, a test-battery, and aswitching device withcontacts and connections by which when the plug is withdrawn from itsnormal position in the switching device the normal ground connection ofthe line is broken and the line is connected to one side of saidtest-battery, substantially as set forth.

In a telephone-exchange system, a metalliccircuit line normally groundedat the subscribers station and one side or branch of which is normallygrounded at the central office, in combination with a switch at thesubscribers station with contacts to open the ground connection therewhile the subscribers telephone is switched for use, a switchplug withcord for said line, a retardation-coil and a switching device into whichthe plug is normally placed,with contacts and connections by which whenthe plug is withdrawn from the device the normal ground connection ofthe line is broken and the line connected to one side of saidretardation-coil, substantially as set forth.

23. In a telephone-exchange system, a metallic-circuit line normallygrounded at the subscribers station and one side or branch of which isnormally grounded at the central office, in combination with a switch atthe subscribers station with contacts to open the ground connectionthere while the subscribers telephone is switched for use, a switchplugwith cord for said line, a testbattery and retardation-coil, and aswitching device into which the plug is normally placed, with contactsand connections by which when the plug is withdrawn from its normalposition in the device, the normal ground connection of the line isbroken and the line is connected to a circuit which contains thetest-battery and retardationcoil,substantially as set forth.

24. In a telephone-exchange system, ametallic-circuit line normallygrounded at the subscribers station and one side or branch of which isnormally grounded at the central office, in combination with a switch atthe subscribers station with contacts to open the ground connectionthere while the subscribers telephone is switched for use, a switchplugwith cord for said line, a test-battery, a switching device into whichthe plug is normally placed, with contacts and connections by which whenthe plug is withdrawn from the device the normal ground connection ofthe line is broken and the line is connected to one side of saidtest-battery, and a test re ceiving instrument connected on one side tothe other side of said test-battery and on its other side to a plug ordevice adapted to be brought into connection with the line,substantially as set forth.

25. In a telephone-exchange system, a metallic-circuit line, normallygrounded at the subscribers station, and one side or branch, of which isnormally grounded at the central office, in combination with a switch atthe subscribers station with contacts to open the ground connectionthere while the subscribers telephone is switched for use, a switchplugwith cord for said line, a test-battery and retardation-coil, aswitching device into which the plug is normally placed,with contactsand connections by which when the plug is withdrawn from the device thenormal ground connection of the line is broken and the line is connectedto one side of a circuit which contains the test-battery andretardation-coil, and a test receiving instrument connected on one sideto the other side of said circuit and on its other side to a plug ordevice adapted to be brought into connection with the line substantiallyas set forth.

In witness whereof I hereunto subscribe my name this 23d day of June,1890.

MILO G. KELLOGG.

\Vitnesses:

EMIL ABENHEIM, ABBOTT L. Mums.

